Bioactive cement

ABSTRACT

A bioactive cement comprises a filler consisting of nonalkali glass powder containing Ca, monomer containing hydrophilic dimethacrylate, a polymerization starter, and a polymerization promotor. The nonalkali glass powder containing Ca comprises a composition by weight of 40-50% CaO, 30-40% SiO 2 , 10-20% P 2  O 5 , 0-10% MgO, and 0-2% CaF 2 . The hydrophilic dimethacrylate is 2,2-bis[4-(3-methacryloxy-2-hydroxy propoxy)phenyl]propane. The bioactive cement is capable of forming a hydroxyapatite layer on a surface of a hardened cement body when the hardened cement body is brought into contact with body fluid.

BACKGROUND OF THE INVENTION

This invention relates to a bioactive cement for bonding or fixing animplant material used in orthopedic and dental fields.

In the orthopedic field, a bone defect due to fracture, bone tumor, orany other disease is dealt with. In some cases, a part of a bone isresected in a surgical operation. In the dental field, a defect of ajawbone may result from extraction of a tooth, a Riggs' disease, and soon. In order to repair such bone defect and to reconstruct the partwhich has been resected, use is made of an implant material comprising asubstance selected from metal, ceramics, and crystallized glass.

It is desired that such implant material is quickly and adaptivelyembedded and fixed in a repair part to be repaired. For this purpose,the implant material must be ground or worked into a shape adapted tothe repair part. However, it is extremely difficult to perform suchgrinding or working with a high precision.

In view of the above, a biocement is generally used together with theimplant material in order to bond and fix the implant material to aliving bone. For example, in the orthopedic field, apolymethylmethacrylate (PMMA) cement has been widely used. In the dentalfield, use has been made of a zinc phosphate cement or a carboxylatecement.

The above-mentioned biocements of various types can make a strong bondwith the implant material. However, those biocements may possibly beloosened from the living bone and frequently induce an inflammatoryreaction in a surrounding tissue.

Under the circumstances, various proposals have been made of theimprovement of the biocement which contains a bioactive substance as afiller so as to provide a chemical bond with the living bone. Forexample, Japanese Patent Publication No. 42384/1979 discloses abiocement comprising a combination of polymethylmethacrylate (PMAA) andK₂ O--Na₂ O--CaO--MgO--SiO₂ --P₂ O₅ crystallized glass powder.

Japanese Patent Prepublication No. 503148/1987 discloses anotherbiocement comprising a combination of2,2-bis[4-(3-methacryloxy-2-hydroxy propoxy)phenyl]propane (hereinafterreferred to as Bis-GMA) base monomer and apatite powder with bioglasspowder added as an optional component.

However, the conventional biocements described above are not yetsatisfactory in bonding condition with the living bone, bondingstrength, mechanical strength, and chemical stability of a hardenedcement body itself which is obtained after completion of a hardeningprocess.

For example, the biocement disclosed in Japanese Patent Publication No.42384/1979 is disadvantageous in that the bonding strength with theliving bone is insufficient. As a result of thorough investigation, thepresent inventors have found out that, once this cement is hardened,body fluid such as cerebrospinal fluid, lymph, and saliva is not allowedto filtrate into the interior of the hardened cement body and thereforethe crystallized glass powder can not exhibit bioactivity. It has alsobeen found out that this is because the biocement uses the monomer(methylmethacrylate, hereinafter abbreviated to MMA) which issubstantially non-hydrophilic.

In addition, the hardened cement body itself has a reduced mechanicalstrength because of two-dimensional polymerization of theabove-mentioned MMA.

Furthermore, the biocement disclosed in Japanese Patent Publication No.42384/1979 comprises, as a filler, the crystallized glass powdercontaining alkali components such as Na₂ O and K₂ O. Accordingly,chemical durability is not excellent and bioactivity is insufficient.

On the other hand, the biocement disclosed in Japanese PatentPrepublication No. 503148/1987 employs, as a hardening agent, Bis-GMAwhich is highly hydrophilic. In accordance with our findings describedabove, it is supposed that the body fluid can easily filtrate in theinterior of the hardened cement body and therefore the biocement canform a chemical bond with the living bone. However, the presentinventors has practically confirmed that a sufficient bonding strengthcan not be achieved with this biocement. This is because the biocementuses a filler comprising apatite which has low bioactivity. In case whenthe apatite powder is exclusively used as the filler, the bonding rateis rather slow and the bonding strength is weak. When the bioglasspowder is additionally used, the bonding rate is increased. However, asilica gel layer, which is thick and fragile, is formed on the surfaceof the bioglass powder because Na₂ O contained in the glass is easilyprecipitated in the form of Na⁺ ion. As a result, a strong bond with theliving bone is difficult to obtain. In addition, the precipitated Na⁺ion increases the pH value of the body fluid. Accordingly, thesurrounding tissue may possibly be adversely affected. Furthermore, thebioglass has a low chemical durability. If this biocement is embedded incontact with the body fluid for a long time, the glass powder is broken.This results in deterioration of the mechanical strength of the hardenedcement body.

SUMMARY OF THE INVENTION

It is an object of-this invention to provide a bioactive cement whichcan be quickly auto-hardened to bond and fix an artificial biomaterial(implant material), which forms a chemical bond with a living bone,which has a stability in a living body for a long time, and which canget rid of deterioration of a mechanical strength.

As a result of extensive research and various experiments, the presentinventors found out that the above-mentioned object is accomplished by acombination of (1) nonalkali glass powder and/or nonalkali crystallizedglass powder containing Ca, and (2) hydrophilic dimethacrylate.

Specifically, a bioactive cement according to this invention comprises afiller consisting of nonalkali glass powder and/or nonalkalicrystallized glass powder containing Ca, a monomer containinghydrophilic dimethacrylate, a polymerization starter, and apolymerization promoter and is capable of forming a hydroxyapatite layeron a surface of a hardened cement body when the hardened cement body isbrought into contact with body fluid.

The nonalkali glass powder and the nonalkali crystallized glass powdercontaining Ca must be able to precipitate Ca²⁺ ion in a living body. Inthis connection, the glass powder or the crystallized glass powder has acomposition consisting by weight of 20-60% CaO, 20-50% SiO₂, 0-30% P₂O₅, 0-20% MgO, and 0-5% CaF₂, preferably, 40-50% CaO, 30-40% SiO₂,10-20% P₂ O₅, 0-10% MgO, and 0-2% CaF₂.

The composition is restricted as specified above because of the groundswhich will presently be described. When CaO is less than 20%, Ca²⁺ ionis difficult to be precipitated. This results in degradation ofbioactivity. When CaO is more than 60%, chemical durability isdeteriorated. When SiO₂ is less than 20%, chemical durability isdeteriorated. When SiO₂ is more than 50%, uniform glass is difficult toobtain. When P₂ O₅ and MgO are more than 30% and 20%, respectively,chemical durability is deteriorated. When CaF₂ is more than 5%,devitrification is increased. This makes it difficult to obtain uniformglass.

In order to provide the hardened cement body having a greater strengthand to obtain high bioactivity, it is desirable that the glass powder orthe crystallized glass powder has a smaller particle size. Preferably,the particle size is not greater than 65 μm.

The glass powder and the crystallized glass powder are restricted tothose containing no alkali component because of the grounds which willpresently be described. When the glass powder or the crystallized glasspowder contains any alkali component, the chemical durability of theglass is considerably degraded. This causes destruction of the glassduring long-term embedment in the living body. As a result, the hardenedcement body itself is also deteriorated in strength. In addition, thealkali component is precipitated and increases the pH value of the bodyfluid. In this event, the surrounding tissue may be adversely affected.Furthermore, when the alkali component is precipitated, a thick andfragile silica gel layer is formed on the surface of the glass powder orthe crystallized glass powder. As a result, it is impossible to obtain astrong bond with the living bone.

In order to provide a stronger bond with polymer, it is preferable tosubject the surface of the glass powder or the crystallized glass powderto a silane coupling treatment. As a silane coupling agent, use isgenerally made of 3-methacryloxy propyl trimethoxy silane, 3-aminoethylaminopropyl trimethoxy silane, 3-glycidoxy propyl trimethoxy silane, andso on.

The hydrophilic monomer used in this invention includes hydrophilicdimethacrylate. The dimethacrylate is a multifunctional monomer andforms a cross-link polymerization structure. Accordingly, the resultantpolymer has a high mechanical strength. It is noted here that thehydrophilic monomer is defined as those containing a hydrophilic groupsuch as an OH group and allowing the body fluid to enter into theinterior of the material (hardened cement body). One preferred exampleof the hydrophilic dimethacrylate is Bis-GMA. Bis-GMA is adapted for usein the living body because it is readily available and harmless in theliving body. However, as described above, use may be made of any othermonomer which contains a hydrophilic group such as an OH group andallows the body fluid to readily enter into the interior of thematerial.

If necessary, other monomer may be contained in addition to thehydrophilic dimethacrylate. When Bis-GMA is exclusively used, thebiocement is often difficult to handle because of high viscosity. Inthis connection, it is preferable to use the additional monomer such astriethylene glycol dimethacrylate (TEGDMA), diethylene glycoldimethacrylate (DEGDMA), and ethylene glycol dimethacrylate (EGDMA).Furthermore, substantially non-hydrophilic monomer may be added ondemand. Addition of the substantially non-hydrophilic monomer is tocontrol a hydrophilic property on the surface of the hardened cementbody. As such a control agent, use is made of 2,2-bis(4-methacryloxyphenyl)propane (BPDMA), 2,2-bis(4-methacryloxy ethoxy phenyl)propane(Bis-MEPP), 2,2-bis(4-methacryloxy polyethoxy phenyl)propane(Bis-MPEPP), or the like.

It is possible to mix the glass powder and the crystallized glass powderwith the monomer at any mixing ratio. However, taking the workability inkneading operation into account, the mixing ratio of the powder to themonomer is desirably within a range between 30:70 and 90:10 by weight.

As the polymerization starter, use may be made of benzoyl peroxide,tri-n-butylborane, or the like. It is possible to induce photopolymerization by the use of a sensitizer such as dl-camphorchinone. Thepolymerization starter may be contained in various manners. The contentof the polymerization starter is selected within a range of 0.01-2 wt %with respect to the total amount of the cement. When the content is lessthan 0.01 wt %, the progress of polymerization is very slow. Thisresults in increase of a hardening time. Thus, workability in kneadingoperation is deteriorated. On the other hand, when the content isgreater than 2 wt % the progress of polymerization is very rapid and thehardening time becomes too short. Thus, in this case also, theworkability in kneading operation is deteriorated.

As the polymerization promoter, use may be made of tertiary amine suchas dimethyl-p-toluidine, diethyl-p-toluidine, and dimethyl aniline. Thepolymerization promoter may be contained in various manners. The contentof the polymerization promoter is selected within a range of 0.01-2 wt %with respect to the total amount of the cement. When the content is lessthan 0.01 wt %, the progress of polymerization is very slow. Thisresults in increase of a hardening time. Thus, workability in kneadingoperation is deteriorated as described above in the case of thepolymerization starter. On the other hand, when the content is greaterthan 2 wt %, the progress of polymerization is very rapid and thehardening time becomes too short. Thus, the workability in kneadingoperation is deteriorated also.

The bioactive cement according to this invention is supplied to a userin the supply form selected from a powder-liquid phase comprising apowder phase material and a liquid phase material and a two-paste phasecomprising two paste phase materials. In the powder-liquid phase, thepowder phase material includes glass powder and/or crystallized glasspowder, and the polymerization starter while the liquid phase materialincludes the monomer and the polymerization promoter. In the two-pastephase, one paste material includes glass powder and/or crystallizedglass powder, the monomer, and the polymerization starter while theother paste material includes glass powder and/or crystallized glasspowder, the monomer, and the polymerization promoter. In use, the usermixes the powder phase material and the liquid phase material or twopaste phase materials with each other. Taking various conditions intoconsideration, one of the above-mentioned supply forms will be selected.Generally, the two-paste phase is desired if a large amount of thepowder component is contained. This is because workability in kneadingoperation is deteriorated when such a large amount of the powdercomponent is kneaded with the hardening liquid. In the bioactive cementaccording to this invention, it is found out that the two-paste phase isdesired when the amount of the powder component is not smaller than 80wt %.

When the filler comprising nonalkali glass powder and/or nonalkalicrystallized glass powder containing Ca, the monomer containing thehydrophilic dimethacrylate, the polymerization starter, and thepolymerization promoter are mixed together at an appropriate mixingratio, polymerization occurs and the mixture is hardened in a short timewithin a range between 3 and 15 minutes.

As a result, a hardened cement body with a high mechanical strength isobtained.

In response to the body fluid filtrating through the surface of thehardened cement body, Ca²⁺ ion is precipitated from the glass powder andthe crystallized glass powder. The precipitated Ca²⁺ ion reacts withPO⁴⁻ ion contained in the body fluid. As a result, a hydroxyapatitelayer similar to the component of the living bone is formed on thesurface of the hardened cement body. Thus, the hardened cement body canbe tightly and readily bonded with the living bone. Since no Na⁺ ion isprecipitated, a thick and fragile silica gel layer is never produced onthe surface. Accordingly, a bonding strength with the living bone isnever decreased.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, description will be made as regards a bioactive cement according toseveral embodiments of this invention.

Table 1 shows various examples (Samples Nos. 1-16) according to thisinvention while Table 2 shows comparative examples (Samples Nos. 17-24).

    __________________________________________________________________________    Table 1-(1)                                                                   Sample No.   1   2   3   4   5   6   7   8                                    __________________________________________________________________________    Powder                                                                              Glass                                                                              A 100 100 100 100 100 100 100 100                                  (wt %)     B                                                                             C                                                                        Crystal-                                                                           A                                                                        lized                                                                              B                                                                        Glass                                                                              D                                                                        Hydroxy-                                                                      apatite                                                                 Monomer                                                                             Bis-GMA                                                                              50  50   40 30  30  30   50  50                                  (wt %)                                                                              Bis-MEPP           20                                                         Bis-MPEPP              20                                                     BPDMA                      20                                                 TEGDMA 50  50   60 50  50  50                                                 DECDMA                          50                                            ECDMA                               50                                        MMA                                                                     Mixing Ratio of Powder/                                                                    85/15                                                                             70/30                                                                             74/26                                                                             77/23                                                                             77/23                                                                             77/23                                                                             70/30                                                                             70/30                                Monomer (wt %/wt %)                                                           Compressive Strength                                                                       180 170 160 170 170 170 165 160                                  (MPa)                                                                         Bonding Strength with                                                                      High                                                                              High                                                                              High                                                                              High                                                                              High                                                                              High                                                                              High                                                                              High                                 Living Bone                                                                   Hardening Time (Minutes)                                                                    5   7   6   5   4   4   7   8                                   __________________________________________________________________________    Table 1-(2)                                                                   Sample No.   9   10  11  12  13  14  15  16                                   __________________________________________________________________________    Powder                                                                              Glass                                                                              A 100 100     50  30                                               (wt %)     B         100         50                                                      C                                                                        Crystal-                                                                           A             50  70      100                                            lized                                                                              B                     50      100                                        Glass                                                                              D                                                                        Hydroxy-                                                                      apatite                                                                 Monomer                                                                             Bis-GMA                                                                              40  50   50 50  50  50   50  50                                  (wt %)                                                                              Bis-MEPP                                                                      Bis-MPEPP                                                                     BPDMA                                                                         TEGDMA 30  50   50 50  50  50   50  50                                        DECDMA 30                                                                     ECDMA                                                                         MMA                                                                     Mixing Ratio of Powder/                                                                    74/26                                                                             35/65                                                                             83/17                                                                             87/13                                                                             77/23                                                                             83/17                                                                             87/13                                                                             83/17                                Monomer (wt %/wt %)                                                           Compressive Strength                                                                       165 160 160 185 160 165 190 165                                  (MPa)                                                                         Bonding Strength with                                                                      High                                                                              High                                                                              High                                                                              High                                                                              High                                                                              High                                                                              High                                                                              High                                 Living Bone                                                                   Hardening Time (Minutes)                                                                    6  10   5   7   7   8   8   10                                  __________________________________________________________________________     A: CaOMgO-SiO.sub.2P.sub.2 O.sub.5                                            B: CaOSiO.sub.2P.sub.2 O.sub.5                                                C: Na.sub.2 OCaO-SiO.sub.2P.sub.2                                             D: K.sub.2 ONa.sub.2 OCaO-MgO-SiO.sub.2P.sub.2 O.sub.5                   

                                      TABLE 2                                     __________________________________________________________________________    Sample No.   17  18  19  20  21  22  23  24                                   __________________________________________________________________________    Powder                                                                              Glass                                                                              A 100                                                              (wt %)     B                                                                             C     100 100 50                                                         Crystal-                                                                           A                                                                        lized                                                                              B                                                                        Glass                                                                              D                 100 100                                                Hydroxy-           50          100 100                                        apatite                                                                 Monomer                                                                             Bis-GMA     50     50   50      50                                      (wt %)                                                                              Bis-MEPP                                                                      Bis-MPEPP                                                                     BPDMA                                                                         TEGDMA      50     50   50      50                                            DECDMA                                                                        ECDMA                                                                         MMA    100     100         100     100                                  Mixing Ratio of Powder/                                                                    70/30                                                                             70/30                                                                             70/30                                                                             70/30                                                                             70/30                                                                             70/30                                                                             70/30                                                                             70/30                                Monomer (wt %/wt %)                                                           Compressive Strength                                                                        50 100  40 110 110  50 115  60                                  (MPa)                                                                         Bonding Strength with                                                                      Null                                                                              Low Null                                                                              Low Low Null                                                                              Low Null                                 Living Bone                                                                   Hardening Time (Minutes)                                                                    8    6  8   7   6   8   8   10                                  __________________________________________________________________________     A: CaOMgO-SiO.sub.2P.sub.2 O.sub.5                                            B: CaOSiO.sub.2P.sub.2 O.sub.5                                                C: Na.sub.2 OCaO-SiO.sub.2P.sub.2                                             D: K.sub.2 ONa.sub.2 OCaO-MgO-SiO.sub.2P.sub.2 O.sub.5                   

Those samples were prepared in the manner which will now be described.

A mixture having a composition consisting by weight of 44.7% CaO, 4.6%MgO, 34.0% SiO₂, 16.2% P₂ O₅, and 0.5% CaF₂ was prepared. The mixturewas melted and vitrified at 1500° C. for two hours into a vitrifiedproduct. Then, the vitrified product was rolled into a compact glassbody. The compact glass body was pulverized in a ball mill andclassified or sieved to obtain glass powder having a maximum particlesize of 65 μm. On the other hand, another compact glass body similarlyformed was fired at 1050° C. for four hours, pulverized in a ball mill,and classified to obtain crystallized glass powder having a maximumparticle size of 65 μm. Each of the glass powder and the crystallizedglass powder was added into aqueous solution of acetic acid containing 1wt % of 3-methacryloxy propyl trimethoxy silane. The solution was heatedand agitated, and then dried at 120° C. for two hours. Thus, the glasspowder A and the crystallized glass powder A with a silane treatmentwere obtained.

Likewise, each of the glass powder B and the crystallized glass powder Bwith a silane treatment was obtained from a mixture having a compositionconsisting by weight of 46.5% CaO, 36.0% SiO₂, 17.0% P₂ O₅, and 0.5%CaF₂.

Furthermore, a mixture having a composition consisting by weight of25.0% Na₂ O, 25.0% CaO, 45.0% SiO₂, and 5.0% P₂ O₅ was processed in themanner similar to the glass powder A to obtain the glass powder C with asilane treatment.

Finally, a mixture having a composition consisting by weight of 5.0% Na₂O, 0.5% K₂ O, 3.0% MgO, 34.0% CaO, 46.0% SiO₂, and 11.5% P₂ O₅ wasprocessed in the similar manner to the crystallized glass powder A toobtain the crystallized glass powder D with a silane treatment.

In the comparative examples, the hydroxyapatite powder having a maximumparticle size of 65 μm was used.

Each sample was prepared by the use of the glass powder and thecrystallized glass powder thus obtained. The powder-liquid phase wasused in Samples Nos. 2-10 and 13 and Comparative Samples Nos. 17-24while the two-paste phase was used in Samples Nos. 1, 11, 12, and 14-16.

In each of the powder-liquid phase samples, 0.4 wt % of benzoyl peroxidewas added with respect to the total amount of the glass powder and thecrystallized glass powder. On the other hand, 0.2 wt % ofdimethyl-p-toluidine was added with respect to the amount of themonomer. The powder phase material and the liquid phase material thusobtained were kneaded with each other to obtain the samples.

In each of the two-paste phase samples, the glass powder and/or thecrystallized glass powder was kneaded with the monomer at the mixingratio indicated in Table 1 and equally divided into two paste materials.In one of the paste materials, 0.6 wt % of benzoyl peroxide was addedwith respect to the amount of the one paste material. In the other pastematerial, 0.2 wt % of dimethyl-p-toluidine was added with respect to theamount of the other paste material. The two paste materials thusobtained were kneaded with each other to obtain the samples.

Each of those samples was evaluated with respect to a compressivestrength for fixation and a bond with the living bone. The results wereshown in Tables 1 and 2.

The compressive strength was measured according to the JapaneseIndustrial Standard Test JIS-T 6602 (for a dental zinc phosphatecement). Each sample was thoroughly kneaded, poured into a desired mold,cured for one hour to be hardened, and taken out from the mold. Thehardened cement body was immersed in a simulated body fluid for 24hours. Then, wet compression strength was measured.

The bond with the living bone was measured as follows. A hole of 2×16 mmwas bored in a tibia condyle of a rabbit. Each sample was kneaded,hardened, and formed into a piece of 10×15×2 mm. The sample piece wasembedded in the hole. After ten weeks, the rabbit was killed to extractthe hardened cement body and the surrounding tissue. Then, separation ofthe cement body and the surrounding tissue was tried. It is holed herethat the bonding strength is represented as "high", "low", and "null"when manual separation was impossible, when the bond was formed butcould be manually separated, and when no bond was observed.

The hardening time was measured according to JIS-T 6602. A needle havinga weight of 300 g and a sectional area of 1 mm² was dropped onto thekneaded mixture of each sample. The hardening time was measured as atime duration until no trace of the needle was formed any longer.

As a result, Samples Nos. 1-16 according to the embodiments of thisinvention exhibited the high compressive strength between 160 and 190MPa. In addition, those samples were very tightly bonded with thesurrounding bone and could not easily be separated by manual force. Noinflammation was observed in the surrounding living tissue.Auto-hardening was performed in a short time between 4 and 10 minutes.

On the other hand, Comparative Samples Nos. 17-24 were hardened in ashort time between 6 and 10 minutes. However, the compressive strengthwas not greater than 115 MPa. As regards the bonding strength with theliving bone, no bond was observed and, if a bond was formed, the bondwas easily separated by manual force. More in detail, ComparativeSamples Nos. 17, 19, 22, and 24 using methylmethacrylate (MMA) as themonomer exhibited the very low compressive strength between 40 and 60MPa. As regards the bond with the surrounding bone, no bond was formedeven in Sample No. 17 using nonalkali glass powder A. ComparativeSamples Nos. 18, 20, 21, and 23 using Bis-GMA as the monomer exhibitedmore favorable results than those using MMA. However, in comparison withSamples according to this invention using nonalkali glass powder ornonalkali crystallized glass powder, the compressive strength and thebonding strength were obviously low.

The above-mentioned facts indicate that a biocement having high strengthand high bioactivity can be obtained by combination of nonalkali glasspowder and/or nonalkali crystallized glass powder and hydrophilicdimethacrylate.

As thus far been described, a bioactive cement according to thisinvention can be quickly auto-hardened to bond and fix an implantmaterial without inducing any inflammatory reaction in a living tissue.In addition, the bioactive cement can be chemically bonded with a livingbone and has a high mechanical strength. Therefore, it is stable for along-term use.

Thus, the bioactive cement is useful for bonding and fixing variouskinds of implant materials. In addition, the bioactive cement is alsouseful as a filler itself for filling a bone defect.

Furthermore, the bioactive cement according to this invention may bepreliminarily hardened for use as an implant material which can beground and worked.

We claim:
 1. A bioactive cement comprising:a filler consisting ofnonalkali glass powder which has a composition consisting by weight of40-50% CaO, 30-40% SiO₂, 10-20% P₂ O₅, 0-10% MgO, and 0-2% CaF₂ ; amonomer containing hydrophilic dimethyacrylate; a polymerization starterfor starting polymerization of said monomer; a polymerization promoterfor promoting polymerization of said monomer; and said bioactive cementforming a hydroxyapatite layer on a surface of a hardened cement bodywhen said hardened cement body is brought into contact with body fluid.2. A bioactive cement as claimed in claim 1,wherein said nonalkali glasspowder is subjected to a silane coupling treatment.
 3. A bioactivecement as claimed in claim 1, wherein said hydrophilic dimethacrylate is2,2-bis[4-(3-methacryloxy-2-hydroxy propoxy)phenyl]propane.
 4. Abioactive cement as claimed in claim 3, wherein said monomer contains,in addition to said hydrophilic dimethacrylate, at least one oftriethylene glycol dimethacrylate (TEGDMA), diethylene glycoldimethacrylate (DEGDMA), and ethylene glycol dimethacrylate (EGDMA). 5.A bioactive cement as claimed in claim 3, wherein said monomer contains,in addition to said hydrophilic dimethacrylate, at least one of2,2-bis(4-methacryloxy phenyl)propane (BPDMA), 2,2-bis(4-methacryloxyethoxy phenyl)propane (Bis-MEPP), and 2,2-bis(4-methacryloxy polyethoxyphenyl)propane (Bis-MPEPP).
 6. A bioactive cement comprising:a fillerconsisting of nonalkali crystallized glass powder which has acomposition consisting by weight of 40-50% CaO, 30-40% SiO₂, 10-20% P₂O₅, 0-10% MgO, and 0-2% CaF₂ ; a monomer containing hydrophilicdimethyacrylate; a polymerization starter for starting polymerization ofsaid monomer; a polymerization promoter for promoting polymerization ofsaid monomer; and said bioactive cement forming a hydroxyapatite layeron a surface of a hardened cement body when said hardened cement body isbrought into contact with body fluid.
 7. A bioactive cement as claimedin claim 6,wherein said nonalkali crystallized glass powder is subjectedto a silane coupling treatment.
 8. A bioactive cement as claimed inclaim 6, wherein said hydrophilic dimethacrylate is2,2-bis[4-(3-methacryloxy-2-hydroxy propoxy)phenyl]propane.
 9. Abioactive cement as claimed in claim 8, wherein said monomer contains,in addition to said hydrophilic dimethacrylate, at least one oftriethylene glycol dimethacrylate (TEGDMA), diethylene glycoldimethacrylate (DEGDMA), and ethylene glycol dimethacrylate (EGDMA). 10.A bioactive cement as claimed in claim 8, wherein said monomer contains,in addition to said hydrophilic dimethacrylate, at least one of2,2-bis(4-methacryloxy phenyl)propane (BPDMA), 2,2-bis(4-methacryloxyethoxy phenyl)propane (Bis-MEPP), and 2,2-bis(4-methacryloxy polyethoxyphenyl)propane (Bis-MPEPP).